@Metcalf, you asked about my system being held just by gravity.
This is a picture of my system clamped in a vise in the horizontal position.
The steel rule is clamped parallel with the jack cylinder.
It’s a bit difficult to tell from the picture, but there is less than 1/8” drop between the two gray painted collars when measured to the rule.
You can also see the safe jack plastic collar that i spoke of in an above post.
IMO it is essential if you plan to use the jack horizontally.
FYI: I have about .005” clearance between the ID and the OD of the parts I fabricated with about 1 1/8” over lap between the pieces. If I was doing this again now that I have the SafeJack collar I would probably increase the overlap to 2”.
I have used this system to push horizontally several times and it worked almost as well as the portapowers we had at work.